This invention is directed to an apple rootstock.
xe2x80x98Malling 9xe2x80x99 rootstock is susceptible to crown and root rots and extremely susceptible to fire blight.
The goal herein was a dwarfing apple rootstock that is resistant to fire blight.
The present invention relates to a new and distinct cultivar of apple tree rootstock, xe2x80x98Geneva 16xe2x80x99, which we discovered in a test planting belonging to New York State Agricultural Experiment Station, Cornell University, Geneva, Ontario County, New York. This discovery is a product of the apple rootstock breeding program of the New York State Agricultural Experiment Station (xe2x80x98Stationxe2x80x99).
Origin: In March, 1981, pollen was collected from a Malus floribunda cv. 821 apple tree and used to pollinate emasculated flowers of a Malusxc3x97domestica cv. Ottawa 3 apple tree growing in Station greenhouse No. 13. The seeds were harvested from fruit produced from this cross and were stratified in November, 1981. After stratification, 560 germinating seeds were planted in a Station greenhouse in January, 1982. When the emerging seedlings were about 2.5 cm tall, they were inoculated with 15 isolates of the fungi Phytophthora cactorum and Phytophthora megasperma, which are causal agents of certain crown and root rots. The flats were flooded to mid-hypocotyl level of the seedlings, and kept at about 23xc2x0 C. for seven days; 127 seedling survived this treatment. The surviving seedlings, when 10 to 15 cm tall, were inoculated in their shoot tips with about 106 cells of isolate Ea 273 of the bacterium Erwinia amylovora, the causal agent of the fire blight disease, using a 26-gauge hypodermic syringe. Three subsequent inoculations with E. amylovora isolate Ea 273 were made in summer and autumn, 1982. All but 14 of the seedlings were discarded for susceptibility to fire blight or were killed by fire blight. The seedling designated 6103FL-016, later tested as CG.16 and now named xe2x80x98Geneva 16xe2x80x99, was very resistant. Lesions that developed from the greenhouse inoculations and later in the field were less than 1 cm long, with some  less than 1 mm long. Later, lesions 2 to 2.5 cm long developed when CG.16 shoots were inoculated with E4001A, a very virulent strain of the bacteria. The survivors were inoculated repeatedly with woolly apple aphids (Eriosoma lanigerum); very susceptible individuals were discarded. Seedings with very small leaves and those displaying either root initials or spines were also discarded.
The plant now designated xe2x80x98Geneva16xe2x80x99 was moderately susceptible to woolly aphids when inoculated with the local wild type. Leaves and fruit of xe2x80x98Geneva16xe2x80x99 are immune to apple scab (Venturia inaequalis) (CG.16""s pollen parent, Malus floribunda cv. 821, carries the Vigene for immunity to scab). Leaves and shoots are moderately susceptible to powdery mildew (Podosphaera leucotricha).
We planted the 14 Erwinia amylovora-resistant seedlings as trench layers on the Station""s Loomis Farm in April, 1983. Rooted liners were harvested in late fall 1984 and were planted in the Station nursery in the spring, 1985. Maiden trees of the cultivars xe2x80x98Topred Deliciousxe2x80x99, xe2x80x98Pagenelli Deliciousxe2x80x99, xe2x80x98Summerland McIntoshxe2x80x99 and xe2x80x98Mutsuxe2x80x99 were produced by grafting onto xe2x80x98Geneva 16xe2x80x99 liners. These trees were subsequently planted in trial orchards at the Station and at the United States Department of Agriculture Appalachian Fruit Research Station, Kearneysville, W. Va.; Washington State University Tree Fruit Research and Extension Center, Wanatchee, Wash; Littletree Orchards, Newfield, N.Y.; and Brown Orchards, Ithaca, NY.
In these test plantings, trees on xe2x80x98Geneva 16xe2x80x99 were similar in size to those on xe2x80x98Malling 9xe2x80x99 EMLA rootstock, based on comparison with the check trees in the same testing plantings. None of the trees on other clones from the xe2x80x98Ottawa 3xe2x80x99xc3x97Malus floribunda family were dwarfed. Trees on xe2x80x98Geneva 16xe2x80x99 began flowering early, usually the second year in the orchard; this wes especially noteworthy for xe2x80x98Mutsuxe2x80x99 cultivar, which in New York normally begins fruiting in the third or fourth year when grafted on the precocity-inducing rootstock xe2x80x98Malling 9xe2x80x99. All of the culivars that have been tested on xe2x80x98Geneva 16xe2x80x99 have demonstrated high production efficiency, similar to that experienced with the very efficient xe2x80x98Malling 9xe2x80x99 rootstock.
Compatibility: We have observed no symptoms of incompatibility with 26 trees of the four fruiting cultivars mentioned above. Besides these, we have grafted xe2x80x98Jonagoldxe2x80x99 on xe2x80x98Geneva 16xe2x80x99; in the nursery we have observed no symptoms of incompatibility. All scionwood used was free from known harmful viruses. Virus sensitivities of xe2x80x98Geneva 16xe2x80x99 are not known.
Propagation: We have propagated xe2x80x98Geneva 16xe2x80x99 asexually by budding and grafting onto seedling and clonal rootstocks; by root cuttings; by hardwood cuttings; by greenwood cuttings; and by conventional layering. These asexual propagules have remained true-to-type with these methods of asexual propagation.
We have also propagated xe2x80x98Geneva 16xe2x80x99 readily in vitro. xe2x80x98Geneva 16xe2x80x99 appears not to be prone to epigenetic changes induced by the growth regulator environment in the tissue culture medium. In layerbeds established with micropropagated xe2x80x98Geneva 16xe2x80x99 plants, rooting has been superior to that observed in conventional layerbeds.
We have also used xe2x80x98Geneva 16xe2x80x99 as a pollen parent in our breeding program; since xe2x80x98Geneva 16xe2x80x99 is highly heterozygous, its seedlings are much different from both parents and from each other, but the excellent resistances to Phytophthora and to Erwinis amylovora transmitted to a substantial percentage of progeny.